1. Field of the Invention
The present invention relates to a semiconductor device including a ceramic multilayer board on which a semiconductor element and a peripheral circuit for the element are mounted and a method for manufacturing the same. More specifically, the present invention relates to a semiconductor device formed by sealing with a resin an array board including a plurality of matrix boards arranged thereon and a method for manufacturing the same.
2. Related Background Art
Recently, in order to cut down on costs and increase the common steps of assembly processes, a method including the steps of mounting a semiconductor element and peripheral circuit components such as a chip resistor, a chip capacitor, a chip inductor, on a ceramic multilayer board, sealing these elements with an epoxy resin, and thereafter breaking or dicing the board into individual pieces has become popular. In general, the epoxy resin is applied on the board by printing a liquid epoxy resin through a printing mask. Although this printing process is easy to conduct, the process has the following problems:                (1) variations in the thickness of resin in products are large,        (2) since resin drips on the periphery of a resin printed portion, a discarded margin becomes necessary,        (3) voids tend to be left in the resin, and        (4) a gap between a chip component and a board cannot be filled.        
The following describes an example of sealing a semiconductor device with resin according to the prior art, with reference to FIG. 9. In FIG. 9, a semiconductor element 1 is mounted on one side of a ceramic multilayer board 2, and chip components 3 including a chip resistor, a chip capacitor, and a chip inductor are mounted on the other side. The semiconductor element 1 is connected by a metal wire 4 to the chip components 3 and the like via another connecting means and through a through hole (not illustrated). The semiconductor element 1 is sealed with a potting resin 5, and the chip components also are sealed with an epoxy resin 6. The ceramic multilayer board 2 is a matrix board on a surface of which an electrode wiring pattern and a component mounting land for mounting a semiconductor element and chip components are arranged repeatedly lengthwise and breadthwise. The semiconductor element 1 is dice-bonded into a cavity 7 in the rear face of the ceramic multilayer board, is connected to an electrode wiring pattern formed within the cavity 7 by the metal wire 4, and is sealed with the potting resin 5. On the surface of the ceramic multilayer board 2, the chip components 3 are mounted. According to the printing resin sealing method, a metal mask 16 having an aperture in a desired shape is aligned with respect to the ceramic multilayer board 2 with a certain gap kept between them, and the liquid epoxy resin 6 is applied thereon using a squeegee 17.
FIG. 10 shows an example where the ceramic multilayer board 2 with components mounted thereon is sealed by a transfer molding method. The ceramic multilayer board 2 with the chip components 3 mounted thereon is placed between an upper mold 91 and a lower mold 92 of a resin sealing mold and a peripheral portion of the board 2 is pinched between the molds to control the position of the board 2. Subsequently, an epoxy resin is filled into a cavity 10 provided in the upper mold 91. This method has the advantages that a dimensional variation is small by virtue of using a mold, the number of generated voids is small because sealing is conducted under the application of pressure to the resin, and therefore the gap between the chip component 3 and the ceramic multilayer board 2 is more likely to be filled. In addition, this method has superior mass-production capability. Such a conventional example is suggested by JP 10(1998)-92979 A. That is to say, as a result of molding with the resin sealing mold shown in FIG. 10, a molded product shown in FIGS. 11A and 11B is obtained. Note here that FIG. 11A is a plan view of the conventional molded product, and FIG. 11B is a cross-sectional view of the same. An epoxy resin 6 is molded on the ceramic multilayer board 2 with a step height.
However, when the transfer molding is conducted with the ceramic multilayer board, the board is warped three-dimensionally due to a distortion resulted from baking at high temperatures and the warp is generated irregularly, and in this method in which a peripheral portion of the board is pinched between the upper and lower molds having flat surfaces, a crack might be generated at the peripheral portion of the board, and in some cases the crack might reach a central portion of the board. For these reasons, molding of the sealing resin is difficult. In addition, when dice-cutting the thus obtained molded product, a problem of becoming vulnerable to a crack occur due to the step height.